| I'm no expert on strawberries, but you haven't gotten an answer, so I did some searching. I found no 'quick and easy' link to send you to, but it looks like you might be dealing with verticillium wilt. Pulled together from a number of different sites, the early symptoms start with brown and curling edges on older leaves. The petioles may turn reddish. As it develops further in the older leaves, the browning also occurs along the main veins of the leaf, and progresses until the leaf dies. As these oldest leaves get worse and die, the somewhat younger ones are getting the brown-curled-edge symptom. It looks like you have cut off some older dead leaves, and the leftover petioles look red. Did these older dying leaves show browning along the veins as they got worse? The sources say that the new leaves might be a little stunted, but otherwise can look normal, until they get to be the somewhat older leaves, and the disease progresses.... Once the plant is infected, the roots and stem are also being damaged unseen, and it eventually kills the entire plant. Best I can do. If this is what the problem is, the prognosis is not good. It's a soil-born disease that, once present, is nearly impossible to cure. The "remedy" suggested everywhere is to plant strawberry varieties that are verticillium-resistant.... If this is what it is, throw them away, but not in the compost. The same fungus infects many other vegetables and ornamentals, including a few trees. Wish I had better news. Hoping I'm wrong. | 
